Pedro J. Valle

Electromagnetic wave scattering from conducting cylindrical structures on flat substrates: study by means of the extinction theorem.

The extinction theorem has been applied to the study of wave scattering from a non-single-valued surface composed of an infinitely long cylinder on a flat substrate, both of which are assumed to be perfect conductors. Cylinder diameters ranging from 0.1 to 4λ (λ being the incident wavelength) are considered. The calculation method is discussed for this kind of geometry. The study has been performed for both S (perpendicular) and P (parallel) polarizations when the direction of an incident Gaussian beam is perpendicular to the cylinder axis and the direction of the scattered wave is in the plane of incidence. The surface-current density on the flat substrate and on the cylinder has also been analyzed.

Optical contrast, topographic contrast and artifacts in illumination-mode scanning near-field optical microscopy

We use a two-dimensional exact numerical simulation and a three-dimensional perturbative analysis to study the coupling between dielectric contrast and topography in the images obtained by illumination-mode scanning near-field optical microscopy. We use a model for the emitting tip, which describes the polarization and confinement effects of a real tip. We analyze the image formation, especially the coupling between topographic and dielectric contrast. In the case of weakly scattering samples, we introduce rigorously the concepts of impulse response and equivalent surface profile. This tool may be useful to describe and understand quantitatively experimental images. Finally, we study the presence of artifacts in the images, due to the coupling between optical scattering and the z motion of the tip in constant-distance operating mode. We put forward the difficulty of predicting the relative weight of the artifact and the purely optical contributions.

Sizing particles on substrates. A general method for oblique incidence

We have developed an experimental light-scattering method to size metallic spherical and cylindrical particles on flat substrates using obliquely incident light. We modify an earlier model to include effects such as the shadowing of the incident and scattered beams. We provide empirical expressions for sizing spheres and cylinders on substrates based on the positions of their minima. The results have been experimentally verified for both types of particle. The extension of the method to oblique incidence angles allows an alternative dynamic procedure.

Experimental study of copolarized light scattering by spherical metallic particles on conducting flat substrates

We present light-scattering experiments for well-characterized random conducting surfaces composed of spherical particles on flat substrates. The experiments were carried out for both sparse (low particle-surface density) and dense targets by using particle sizes of the order of the incident wavelength (λ = 0.633 μm). We analyzed both small incidence angles and grazing incidence and present the results for both p and s polarizations. Also, we present the results of computer-simulated light-scattering experiments based on the extinction theorem for a one-dimensional, perfectly conducting surface model for comparison with the experimental results. This model is composed of an array of parallel cylinders upon a flat substrate whose separations follow an exponential distribution corresponding to a pure Poisson process. The possible relevance of these results to radar scattering from the sea surface is also briefly discussed.

SCATTERING BY A METALLIC CYLINDER ON A SUBSTRATE : BURYING EFFECTS

Experimental measurements of the light scattered from a metallic circular cylinder, with a section diameter comparable with the incident wavelength, upon a metallic flat substrate are presented. The validity of the theoretical numerical calculation obtained from a one-dimensional model based on Maxwells coupled integral equations for real metals is demonstrated by comparison with the experimental results. The theoretical model is able to reproduce a geometric feature as the partial burying of the cylinder in the substrate because of the sputtering process.

METALLIC PARTICLE SIZING ON FLAT SURFACES : APPLICATION TO CONDUCTING SUBSTRATES

A fast and accurate microsizing method is introduced and analyzed for metallic protuberances on flat substrates. It is based on the measurement of the minima angular positions of the S‐polarized far field scattering patterns at normal incidence. The proposed method has been theoretically and experimentally checked for both cylindrical and spherical metallic protuberances on conducting flat substrates. The excellent agreement between theory and experiment proves the efficiency of the method. We also comment on the application of this method for other protuberance geometries and different substrates other than metallic.

Backscattering from particulate surfaces: experiment and theoretical modeling

The copolarized backscattered intensity from surfaces composed of metallic particles on conducting flat substrates is analyzed experimentally as a function of the incidence angle. The analysis is done for particle sizes smaller than, comparable to, and larger than the incident wavelength (0.633 μm) and for low particle surface densities. Numerical calculations based on the extinction theorem for a onedimensional surface model consisting of an infinitely long cylinder located on a flat substrate for the same optical constants used in the experiment are also presented for qualitative comparison with the experimental results. This serves to analyze the effect of particle aggregation. For the surfaces with particles smaller than the incident wavelength, conclusions are drawn concerning the possible relevance of this study in radar wave scattering from the sea surface.

Visual axial PSF of diffractive trifocal lenses

The ophthalmic applications of a diffractive trifocal lens design with adjustable add powers and light distribution in the foci are investigated. Axial PSFs of the trifocal lenses are calculated and analyzed as a function of the design parameters and the eye pupil size. The optical performance in actual eyes is also simulated by including the measured ocular wave aberration functions of human eyes in the calculation of transverse and axial PSFs, and Strehl ratio axial variation. The effect of the polychromatic character of natural light has also been considered. The calculus and simulation method of this paper can be applied for the design and analysis of any other kind of diffractive or refractive multifocal contact or intraocular lens.

Near field by subwavelength particles on metallic substrates with cylindrical surface plasmon excitation

Abstract The near electromagnetic field scattered by a spherical subwavelength particle on a flat metallic substrate is calculated when the incident light is a plane monochromatic linearly polarized wave. The complete solution to the scattering problem that we consider includes the possible surface wave components of the field. Cylindrical surface plasmon-polaritons are shown to be excited by the particle on the substrate when this is metallic and the particle is close enough. The shape of the field associated to the surface plasmon-polariton depends on the incident polarization and angle of incidence. In a real situation, the plasmon field interferes with the incident field. The spatial distribution of the interference pattern is analyzed in terms of the incident polarization and the angle of incidence and differences from the case of bulk propagating waves are shown. Incident polarization parallel to the plane of incidence is proved to be more efficient than the perpendicular one for surface plasmon generation because of the vertical component of the particle dipole moment. The propagation characteristics of the cylindrical surface waves (wave number, phase) are obtained from the interference pattern.

Multiple scattering in particulate surfaces: Cross-polarization ratios and shadowing effects

Abstract Multiple scattering and cross-polarization effects, as well as their relationship with the surface particle density and the angle of incidence, are experimentally analyzed for metallic particulate surfaces. The analysis includes measurements (in the plane of incidence) of the co- and cross-polarized scattered intensities from surfaces constituted by spherical metallic particles (diameter of 1.1 μm approximately) on conducting flat substrates, illuminated by a HeNe laser (λ = 0.633 μm). Shadowing is specially studied through its effects on the cross-polarization ratios for high values of either the angle of incidence or the surface particle density.